Subj : HVYSNOW: US Winter Storm To : All From : Dumas Walker Date : Mon Jan 15 2024 08:39 am FOUS11 KWBC 151012 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 511 AM EST Mon Jan 15 2024 Valid 12Z Mon Jan 15 2024 - 12Z Thu Jan 18 2024 ....East Texas, Lower MS Valley, Deep South, TN Valley, Appalachians through Northeast... Days 1-3... A vort max over the TX Panhandle will zip east today on the tail of a potent WSWly jet which will promote further low level moisture flow from the western Gulf and produce light precip over south-central and East TX through the Deep South. Surface cold air advection will continue to bring these areas below freezing with a light glaze likely through this swath and 20% probs for >0.1" ice over east TX/northern Louisiana/central MS as well as far northeast AL/northwest GA. To the north, the arctic air will be much deeper, supporting all snow from eastern AR eastward across northern MS and through much of TN and the southern Appalachians. Relatively high SLRs (~12-16:1) would favor several inches of snow that will continue to be enhanced by frontogenetical banding as the entire system shifts eastward ahead of a sharpening trough axis rounding the sprawling low centered up over Ontario. Day 1 snow probs for >4" are 40%-70% from eastern TN up far western VA into central WV with lower probs over the northern VA Blue Ridge and north-central MD. Coastal low development off the Mid-Atlantic coast begins late tonight which quickly rides north in the right entrance to the intensifying SWly jet just inland of the Northeastern Seaboard. Day 1.5 snow probs for >4" are around 20% for eastern PA/northern NJ/southern NY into southwest New England and then they increase farther north for Day 2 probs with northern and eastern Maine generally 40-60% where the coastal low is rapidly deepening as it moves north just off the New England coast. ....Colorado Rockies onto Central High Plains... Day 1... Shortwave trough rounding sprawling/deep low centered over northern Ontario shifts southeast over the CO Rockies today before swinging east over the central Plains this evening. 1050mb surface high pressure is on its heels this morning over northern MT. Snow continues through this afternoon over the CO Rockies with light to locally moderate snow bands shifting east in the strengthening Wly jet across KS/MO/IL/IN today through tonight. Day 1 snow probs are 40-60% for an additional >6" on the central CO Rockies with low probs for >2" east from the Palmer Divide across KS. ....Prolonged Great Lake Effect Snow... Days 1-3... Expansive upper low established itself over far northern Ontario today and lingers through Wednesday. A wrapping vort/wave crosses the Great Lakes from west to east this evening through Tuesday. The prolonged cyclonic flow across the Great Lakes maintains the multi-day lake effect snow with NWly flow and multi-bands over the western Lakes and Wly to WSWly flow and single bands for the eastern Lakes. Robust single bands off Lakes Erie/Ontario continue for nearly all typical lake belts, with minor variations continuing as well as some disruption from the vort passage Tuesday morning. PWPF do not handle the small phenomena of LES well, but for the Erie/Ontario single bands, Day 1 is generally north of Day 2 as the flow veers more from WSWly to Wly. Day 3 is back north a bit and much more intense with high probs for >8" off both. Otherwise, it's the Keweenaw Peninsula that gets enough snow Days 1/2 to show up in the PWPF. ....Northwest... Days 2/3... A one-two punch of mid-level waves reaches the Pacific Northwest late Tuesday and on Wednesday. The first is a southern stream compact low that slices east through the northeastern Pacific ridge and the second is a sharp northern stream trough that slowly shifts south down the Alaskan Panhandle tonight/Tuesday and the BC coast Tuesday night/Wednesday before shifting southeast down the northern Rockies Wednesday night. Ample moisture plume leading the compact low surges inland across the PacNW coast Tuesday to the northern Rockies Tuesday night with snow levels shooting up to 8000ft by Tuesday evening, though these quickly drop below 5000ft under the low Tuesday night. However, the Arctic-sourced air that remains over northern OR/western WA will persist under the milder air aloft move into the region Tuesday. A wintry mix of snow/sleet to freezing rain is likely over the lower Columbia area including the Portland metro where Day 2 ice probs for >0.1" ice are 30-60% along with 10-20% probs for >0.25" ice. Farther inland, deep cold air will remain entrenched which favors higher SLRs with Day 2 snow probs for >6" 10-40% over the WA Cascades and the Sawtooths near Boise. Then the second wave moving into the interior Northwest late Wednesday will further aide the inland surge of Pacific moisture with widespread mountains snows over the Cascades and northern/central Rockies where day 3 snow probs for >6" are 40-60%. Day 3 probs for >12" are 50-90% for the WA Cascades and the Bitterroots. Jackson ***Key Messages for Southern and Eastern Winter Storm*** --Southern Wintry Mix Continues Today Areas of sleet and freezing rain will continue to impact areas from south-central Texas through the lower Mississippi Valley and into eastern Tennessee. With arctic air in place hazardous travel can be expected. --Snow over the Southern Appalachians through Mid-Atlantic today into Tuesday Areas of snow will continue over Tennessee, the southern Appalachians and Mid-Atlantic today into Tuesday. Plan on slippery roads and difficult travel conditions. $$ --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .